Multilevel metallization systems are becoming common in the electronics industry to reduce the space required for metal interconnections. In such systems, a first metal layer is deposited on a suitable substrate and defined. A layer of dielectric material is deposited thereover and vias are formed therein, thus exposing a portion of the first metal layer and/or the substrate. A second layer of metal is deposited thereover and defined to form the remaining portion of the interconnection system. A final layer of dielectric material is deposited thereover to insulate and protect the system.
Typically, substrates to be coated with multilevel metallization have uneven topography, e.g device structures or epitaxial silicon islands on their surfaces. It is therefore generally preferred to deposit a planarizing layer prior to deposition of the first metal layer, so that the layer of resist material which is used to define the metal layer may itself be patterned with utmost accuracy. This becomes more important as line widths drop to one micrometer or less. It is therefore advantageous that the dielectric materials have good planarizing properties.
Certain glasses, i.e., silicon dioxide and phosphosilicate glass (PSG) are conventional in the electronics industry for dielectric insulation between patterned layers of refractory metallization, i.e. refractory conductors. Borophosphosilicate glass (BPSG) is an unexpectedly superior dielectric material in such systems as disclosed in copending application Ser. No. 526,623, filed Aug. 26, 1983, the disclosure of which is incorporated herein by reference. In addition to other desireable properties, phosphosilicate glass and borophosphosilicate glass can be heated to flow or reflow them in order to obtain a smooth surface topography. It is necessary, however, when a structure contains a plurality of such dielectric materials that flowing a given layer does not cause remelting of previously deposited layers. A system of dielectric glass compositions which meets this criteria and which, unexpectedly, remains stable against mutual flow and dissolution is provided herein.